⚠ NEVER DRIVE AFTER DRINKING — This calculator is for educational purposes ONLY. It cannot determine if you are safe or legal to drive.
BAC Calculator
Estimate your Blood Alcohol Content from drinks, weight, sex, and time. Understand impairment levels and roughly how long until sober.
Widmark
FORMULA
0.08%
US LEGAL LIMIT
~5hr
PER DRINK
±0.015
HOUR
BAC Estimator
Widmark Formula — For education only
2 beers ≈ 28g pure alcohol
Estimated BAC
0.032%
No measurable impairment
~2h 8m until BAC returns to 0.00%
Educational estimate only — never a substitute for a breathalyzer, and never a reason to drive.
IMPAIRMENT REFERENCE
BAC Levels & Impairment Effects
How blood alcohol content affects behavior, cognition, and physical ability at each level.
| BAC Level | Level Name | Typical Effects | Driving Safety |
|---|---|---|---|
| 0.01-0.03% | Subtle | A light sense of warmth and mild mood lift. Most people notice almost no change in how they act or feel. | Reaction time can already begin to soften — reasonably safe for most adults, but never guaranteed. |
| 0.04-0.06% | Relaxed | Muscles loosen and inhibitions drop. Judgment and coordination start to slip, even if it doesn't feel that way. | Measurable impairment is setting in — this is where many countries' driving limits already sit. |
| 0.07-0.09% | Impaired | Reflexes, balance, and judgment are clearly affected. A false sense of confidence is common. | Illegal to drive in the US and most countries at 0.08% — reaction time and tracking are unreliable. |
| 0.10-0.12% | Significant | Speech slurs, motor control degrades further, and emotions can swing sharply. | High crash risk — steering, braking, and hazard response are all meaningfully slower. |
| 0.13-0.15% | Seriously Impaired | Vision blurs, balance becomes unreliable, and nausea is common. | Extremely dangerous — this level is involved in a large share of fatal alcohol-related crashes. |
| 0.16-0.19% | Very Drunk | Dysphoria, disorientation, and nausea are typical. Memory blackouts can begin at this range. | Operating any vehicle is unsafe for you and everyone around you. |
| 0.20-0.25% | Stupor | Standing or walking unassisted becomes difficult. Confusion and blackout are likely. | Medical risk is rising — this is no longer just a driving question. |
| 0.30%+ | Unconscious | Loss of consciousness is possible, along with a real risk of choking if vomiting occurs. Life-threatening. | This is a medical emergency — call for help immediately. |
LEGAL LIMITS
BAC Legal Limits by Country
Legal driving limits vary significantly worldwide. Zero tolerance is increasingly common for young and commercial drivers.
| Country / Region | Standard Limit | Young / New Drivers | Commercial Drivers |
|---|---|---|---|
| 🇺🇸United States | 0.08% | 0.00-0.02% (varies by state) | 0.04% |
| 🇨🇦Canada | 0.08% | 0.00% (most provinces) | 0.04% |
| 🇬🇧United Kingdom | 0.08% | 0.08% (0.05% in Scotland) | 0.00% |
| 🇩🇪Germany | 0.05% | 0.00% (under 21 or <2 yrs licensed) | 0.00% |
| 🇫🇷France | 0.05% | 0.02% (probationary license) | 0.02% |
| 🇦🇺Australia | 0.05% | 0.00% (L/P plate holders) | 0.00% |
| 🇯🇵Japan | 0.03% | 0.03% | 0.03% |
| 🇸🇪Sweden | 0.02% | 0.02% | 0.02% |
The Only Safe Choice After Drinking: Don't Drive
No calculator — this one included — can tell you whether you are safe or legal to drive. Individual variation in metabolism, food intake, medications, fatigue, and genetics means two people with identical calculated BAC levels can be very differently impaired in reality. If you've been drinking, take a cab, call a rideshare, use a designated driver, or stay where you are. Don't drive.
📜 The Widmark Formula
Swedish physician Erik M.P. Widmark developed this formula in the 1920s, and it remains the forensic and medical standard for BAC estimation used in legal proceedings worldwide. It accounts for the distribution of alcohol through the body's water content using a sex-specific factor: 0.73 for men and 0.66 for women on average, reflecting typical differences in body water proportion and liver enzyme activity between the sexes.
🥃 What Is a Standard Drink?
In the US, one standard drink contains about 14 grams (0.6 fl oz) of pure alcohol. That's roughly a 12oz regular beer (5% ABV), a 5oz glass of wine (12% ABV), or a 1.5oz shot of 80-proof spirits (40% ABV) — all three contain nearly identical pure alcohol despite very different pour sizes. Many drinks contain more than one standard drink: a 16oz craft IPA at 8% ABV is over two standard drinks, and a generous restaurant wine pour is often 1.5-2x a standard glass.
How BAC Is Calculated — The Widmark Formula
Blood Alcohol Content (BAC) is the concentration of alcohol in the bloodstream, expressed as grams of alcohol per 100 milliliters of blood. This calculator uses the Widmark formula — the forensic and medical standard for BAC estimation.
BAC% = (A / (W × r × 1000)) × 100 − (0.015 × H) Where: A = Total grams of pure alcohol consumed W = Body weight in kilograms (lbs ÷ 2.20462 if entered in pounds) r = Widmark factor — 0.73 for men, 0.66 for women H = Hours since your first drink 0.015 = Average BAC eliminated by the body per hour Example — 180lb (81.6kg) male, 2 beers (28g alcohol), 1 hour: BAC = (28 / (81.6 × 0.73 × 1000)) × 100 − (0.015 × 1) BAC = 0.047% − 0.015% ≈ 0.032%
Important Limitations
The Widmark formula produces an estimate only. It cannot account for food in the stomach (which slows absorption and can reduce peak BAC), drink speed (faster drinking raises peak BAC), carbonation in mixers (which speeds absorption), medications, liver health, genetics, age, or body composition. Only a certified breathalyzer or blood test can measure your actual BAC — never this or any other calculator.
— FAQ